Taylor and Hulse conducted their prizewinning research on pulsars while Taylor was a professor at Amherst and Hulse was his graduate student. In 1974, using the large radio telescope at Arecibo, Puerto Rico, they discovered a pulsar (a rapidly spinning neutron star) emitting radio pulses at intervals that varied in a regular pattern, decreasing and increasing over an eight-hour period. They concluded from these signals that the pulsar must be alternately moving toward and away from the Earth—i.e., that it must be orbiting around a companion star, which the two men deduced was also a neutron star.

Their discovery of the first binary pulsar, PSR 1913 + 16, provided an unprecedented test of Albert Einstein’s theory of gravitation, which, according to the general theory of relativity, predicts that objects accelerated in a strong gravitational field will emit radiation in the form of gravitational waves. With its enormous interacting gravitational fields, the binary pulsar should emit such waves, and the resulting energy drain should reduce the orbital distance between the two stars. This could in turn be measured by a slight, gradual reduction in the timing of the pulsar’s distinctive radio emissions.

Taylor and Hulse timed PSR 1913 + 16’s pulses over the next few years and showed that the two stars are indeed rotating ever faster around each other in an increasingly tight orbit, with an annual decrease of about 75 millionths of a second in their eight-hour orbital period. The rate at which the two stars are spiraling closer together was found to agree with the prediction of the theory of general relativity to an accuracy of better than 0.5 percent. This finding, reported in 1978, provided the first experimental evidence for the existence of gravitational waves and gave powerful support to Einstein’s theory of gravity. In the following years, Taylor continued making careful measurements of the orbital period of PSR 1913 + 16, and his research group went on to discover several other binary pulsars.

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...pulses of radio-frequency radiation. These pulsars have been used as galactic clocks to study other phenomena. By studying the spin-down rate of a pulsar in close orbit with a companion star, Joseph Taylor, an American astrophysicist, was able to show that a significant amount of the rotational energy lost was due to the emission of gravitational radiation. The existence of gravitational...

...producing a series of pulses corresponding to the rotation of the neutron star, much like the beacon from a rotating lighthouse lamp. In 1974, using the Arecibo Observatory, American astronomers Joseph Taylor and Russell Hulse observed a binary pulsar (two pulsars in orbit around each other) and found that their orbital period was decreasing because of gravitational radiation at exactly the...

...that the two stars are spiraling toward one another at exactly the predicted rate. Gravitational radiation is the only known means by which that could happen. (American physicists Russell Hulse and Joseph H. Taylor, Jr., won the Nobel Prize for Physics in 1993 for their discovery of PSR 1913+16.)

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(born 1941). U.S. radio astronomer and physicist Joseph Hooton Taylor, Jr., cowinner (with Russell A. Hulse) of the 1993 Nobel Prize in Physics, was born in Philadelphia, Pennsylvania, on March 24, 1941. Taylor earned a Ph.D. in astronomy from Harvard University in 1968 and then joined the faculty of the University of Massachusetts at Amherst the following year. From 1977 to 1981 he served as the associate director of the Five-College Radio Astronomy Observatory in Massachusetts. In 1980 Taylor joined the staff of Princeton University and subsequently became the James S. McDonnell Distinguished University Professor of Physics. Taylor won the Nobel Prize for helping to discover the first binary, or double, pulsar along with his graduate student Hulse in 1974. They called this pulsar PSR 1913 + 16. The discovery of this pulsar allowed researchers to test Einstein’s general theory of relativity and alternative theories of gravity. Because of the speed and stability of its rotation, pulsars can also provide a better time standard than even the most accurate atomic clock. Taylor’s research group went on to discover several other binary pulsars.